This invention pertains to a vehicular parking system in operative combination with a service brake system for positively holding a stopped vehicle in a stationary position. The combined parking and service brake system according to the invention has particular utility in conjunction with earthmovers such as those equipped with a bucket or like implement assembly.
The first and foremost requirement of the parking system in earthmovers of the type in question is the capability of firmly holding the vehicle stationary during excavating, loading and similar operations, in spite of great reactive forces exerted on the vehicle via the implement assembly. Some such vehicles incorporate an "air over" or air-assisted hydraulic brake system, in combination with a negative brake mechanism on the propeller shaft as a parking brake. This known parking system is insufficient for positively holding the vehicle in a fixed positon during earthmoving operations. Even if the propeller shaft is braked, the axle shafts coupled thereto via a differential tend to rotate by the noted reactive forces.
The most practical solution to the problem is to apply not only the parking brake but also the service brakes for immobilizing the vehicle during earthmoving operations. In carrying this solution into practice, moreover, it is desired that both parking and service brakes be readily applied and released by manipulation of a single control means.